The Steam release of Redneck Rampage Rides Again unfortunately lacks the 8-track CDDA soundtrack and runs on DOSBox. However, one can get a much smoother experience with added music and Steam overlay by using a source port that supports widescreen resolutions and additional tweaking.
This guide was prepared with Raze in mind, a source port that combines various Build Engine ones in a single package with stability and renderer improvements and using several GZDoom systems as a backend. It is a dependable, feature-rich and user-friendly port that can be used to play all the Build Engine games, excluding TekWar and both Witchavens. In Redneck Rampage's and its sequel's case, it is based on Rednukem code.
SteamEdit, a nifty utility for editing local Steam data, is also needed to enable the overlay while using the port.
Get the latest versions of Raze and SteamEdit here[github.com]and here.[steamedit.tg-software.com]
Also download the additional soundtrack package I prepared, here.[drive.google.com]
The soundtrack is ripped by me (-q9, 320kbps) and comes fully tagged with cover art.

1) Open the folder titled 'Again' found in the installation directory and copy REDNECK.GRP and REDINT.MVE to somewhere else. These two are the only files the source port needs (the latter being the optional introductory sequence) so once you get them copied, delete all the files in the installation directory to have a cleaner setup.
2) Unzip the contents of both the Raze package and the soundtrack package provided above to the installation directory (while keeping the folder structure intact) and copy back REDNECK.GRP and REDINT.MVE. The resulting setup should look like this:
3) While Steam is running in the background, launch SteamEdit (it can be run directly from the zipped archive). Find Redneck Rampage in the drop-down list and click on 'Edit Launch'. The executable line in the secondary window should read Launch Redneck client.bat. Erase that line and type raze.exe instead. Click on 'OK' to close the window and then click on 'Save & Refresh' in the primary one. Steam should close and restart by itself.
At this point clicking on the 'Play' button in the Steam Library should directly launch Raze running the game. Note that uninstalling / reinstalling the game or a Steam client update may revert the changes you make through SteamEdit, so keep the tool somewhere handy in case you need to do the last step again.

As an advanced option, if you own both Redneck Rampage and the sequel RR Rides Again you can form a complete pack tied to a single executable. In a nutshell:
With the above setup, running the port should display the Game Selection window with three options: Redneck Rampage, RR Rides Again and RR: Suckin' Grits on Route 66.

Be sure to check out the extensive options menu offered by Raze before hitting the road.
Upon first launch, Raze creates an .ini file in the installation directory (raze-YourUsername.ini) that holds your configuration and can be transferred between the installation folders of the games supported by the port to keep your non-game specific preferences intact.
Your saves are kept under the Saves folder which is also created by Raze upon first running it.
As pointed out in detail by the user MetHy in this post[forums.duke4.net]over at Duke4.net forums, the kill counter is more-or-less broken in the original code and it remains so in the port.
The 8-track player, as named by the developers, plays all the music tracks in succession and on repeat. As the name implies however, it is limited to eight tracks only. Raze keeps the code intact, so even if you have more than that in the music folder, the ones named track10 and onwards are not played. Still, it is possible to mix and match the soundtracks of both games by appropriate naming to your heart's content. On my part, I like the original's soundtrack more than the sequel's (since half of the latter consists of short instrumentals) so I use it for both of them.
If you ever get stuck, Jon Hurt's oldish website Totally Redneck[jonhunt.com]has text-based walkthroughs and secret guides for all the games in the series.
Instructions for playing the original game and its expansion pack through Raze following the same format seen here has also been published alongside this one. Check it out if you are in for a completionist's run:
'Are ya ready boys?!'