@scottalanmiller Thanks!

@JaredBusch I find it interesting that my installer did in fact install those two repositories, but still fails. What might I need to do to get this to work?

@JaredBusch Apparently mine did not do this step.

I attempted to install via the install.sh script and it got most of the way through without error. Then, toward the end of the script, I get this:
----Begin Paste----

Setting up hosts file.

Starting the apache server.

Created symlink from /etc/systemd/system/multi-user.target.wants/httpd.service to /usr/lib/systemd/system/httpd.service.

Configuring .env file.

All settings correct for using Composer
Downloading...

Composer (version 1.4.2) successfully installed to: /var/www/html/snipeit/composer.phar
Use it: php composer.phar

Do not run Composer as root/super user! See https://getcomposer.org/root for details
Loading composer repositories with package information
Installing dependencies from lock file
Your requirements could not be resolved to an installable set of packages.

Problem 1
- This package requires php >=5.5.9 but your PHP version (5.4.16) does not satisfy that requirement.
Problem 2
- Installation request for aws/aws-sdk-php 3.19.2 -> satisfiable by aws/aws-sdk-php[3.19.2].
- aws/aws-sdk-php 3.19.2 requires php >=5.5 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 3
- Installation request for aws/aws-sdk-php-laravel 3.1.0 -> satisfiable by aws/aws-sdk-php-laravel[3.1.0].
- aws/aws-sdk-php-laravel 3.1.0 requires php >=5.5.9 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 4
- Installation request for barryvdh/laravel-debugbar V2.2.3 -> satisfiable by barryvdh/laravel-debugbar[V2.2.3].
- barryvdh/laravel-debugbar V2.2.3 requires php >=5.5.9 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 5
- Installation request for classpreloader/classpreloader 3.0.0 -> satisfiable by classpreloader/classpreloader[3.0.0].
- classpreloader/classpreloader 3.0.0 requires php >=5.5.9 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 6
- Installation request for guzzlehttp/guzzle 6.2.1 -> satisfiable by guzzlehttp/guzzle[6.2.1].
- guzzlehttp/guzzle 6.2.1 requires php >=5.5 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 7
- Installation request for guzzlehttp/promises 1.2.0 -> satisfiable by guzzlehttp/promises[1.2.0].
- guzzlehttp/promises 1.2.0 requires php >=5.5.0 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 8
- Installation request for laravel/framework v5.2.45 -> satisfiable by laravel/framework[v5.2.45].
- laravel/framework v5.2.45 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.
Problem 9
- Installation request for laravelcollective/html v5.2.4 -> satisfiable by laravelcollective/html[v5.2.4].
- laravelcollective/html v5.2.4 requires php >=5.5.9 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 10
- Installation request for league/csv 7.2.0 -> satisfiable by league/csv[7.2.0].
- league/csv 7.2.0 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.
Problem 11
- Installation request for maknz/slack dev-master -> satisfiable by maknz/slack[dev-master].
- maknz/slack dev-master requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.
Problem 12
- Installation request for spatie/db-dumper 1.5.1 -> satisfiable by spatie/db-dumper[1.5.1].
- spatie/db-dumper 1.5.1 requires php ^5.5|^7.0 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 13
- Installation request for spatie/laravel-backup 3.8.1 -> satisfiable by spatie/laravel-backup[3.8.1].
- spatie/laravel-backup 3.8.1 requires php ^5.5|^7.0 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 14
- Installation request for symfony/console v3.0.9 -> satisfiable by symfony/console[v3.0.9].
- symfony/console v3.0.9 requires php >=5.5.9 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 15
- Installation request for symfony/debug v3.0.9 -> satisfiable by symfony/debug[v3.0.9].
- symfony/debug v3.0.9 requires php >=5.5.9 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 16
- Installation request for symfony/event-dispatcher v3.1.3 -> satisfiable by symfony/event-dispatcher[v3.1.3].
- symfony/event-dispatcher v3.1.3 requires php >=5.5.9 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 17
- Installation request for symfony/finder v3.0.9 -> satisfiable by symfony/finder[v3.0.9].
- symfony/finder v3.0.9 requires php >=5.5.9 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 18
- Installation request for symfony/http-foundation v3.0.9 -> satisfiable by symfony/http-foundation[v3.0.9].
- symfony/http-foundation v3.0.9 requires php >=5.5.9 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 19
- Installation request for symfony/http-kernel v3.0.9 -> satisfiable by symfony/http-kernel[v3.0.9].
- symfony/http-kernel v3.0.9 requires php >=5.5.9 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 20
- Installation request for symfony/process v3.0.9 -> satisfiable by symfony/process[v3.0.9].
- symfony/process v3.0.9 requires php >=5.5.9 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 21
- Installation request for symfony/routing v3.0.9 -> satisfiable by symfony/routing[v3.0.9].
- symfony/routing v3.0.9 requires php >=5.5.9 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 22
- Installation request for symfony/translation v3.0.9 -> satisfiable by symfony/translation[v3.0.9].
- symfony/translation v3.0.9 requires php >=5.5.9 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 23
- Installation request for symfony/var-dumper v3.0.9 -> satisfiable by symfony/var-dumper[v3.0.9].
- symfony/var-dumper v3.0.9 requires php >=5.5.9 -> your PHP version (5.4.16) does not satisfy that requirement.
Problem 24
- laravel/framework v5.2.45 requires ext-mbstring * -> the requested PHP extension mbstring is missing from your system.
- watson/validating 2.2.2 requires illuminate/contracts ~5.0 <5.3 -> satisfiable by laravel/framework[v5.2.45].
- Installation request for watson/validating 2.2.2 -> satisfiable by watson/validating[2.2.2].

To enable extensions, verify that they are enabled in your .ini files:
- /etc/php.ini
- /etc/php.d/curl.ini
- /etc/php.d/dom.ini
- /etc/php.d/fileinfo.ini
- /etc/php.d/gd.ini
- /etc/php.d/json.ini
- /etc/php.d/pdo.ini
- /etc/php.d/pdo_sqlite.ini
- /etc/php.d/phar.ini
- /etc/php.d/posix.ini
- /etc/php.d/sqlite3.ini
- /etc/php.d/sysvmsg.ini
- /etc/php.d/sysvsem.ini
- /etc/php.d/sysvshm.ini
- /etc/php.d/wddx.ini
- /etc/php.d/xmlreader.ini
- /etc/php.d/xmlwriter.ini
- /etc/php.d/xsl.ini
- /etc/php.d/zip.ini
You can also run php --ini inside terminal to see which files are used by PHP in CLI mode.

If you want mail capabilities, edit /var/www/html/snipeit/.env and edit based on .env.example

Open http://monitor.alaska.lan to login to Snipe-IT.

• Cleaning up...
• Finished!
  ----End Paste----

So, in short, it appears that the script relies on PHP being at a version higher than the one that ships with CentOS 7.3. Has anyone found a way around this yet? I've seen a few different HOWTO's where it's mentioned to install the remi or webtatic repo's to get the higher versions of PHP, but composer continues to complain. Thankfully, this was a VM and I was able to create a snapshot before making changes from the baseline.