Hi Jeff -- since I have a travel trailer I'll leave the technical side of your question to others. My purpose is to simply welcome you to the forum and suggest taking a few minutes to read the Welcome Letter as it (hopefully) will provide a jump start to getting the most from your time here on the forum.

Howard

Welcome to the forum and I echo what howson suggests.
There is lots of info on Youtube on the "how to" part. Just take that info with a box of salt. Many places with info are thinly veiled advertisements.
There are many places that will sell what ever you desire. Your favorite search engine is your friend. I would start by searching on the chosen pin box.
The air-cushion pin boxes dictate that you have a ready source of compressed air. This is another rabbit hole.

I, too, am looking at a replacement pin box for my 381MS. I am thinking more passive cushioning.

Steve

Changing the box out should not be that difficult. I did the stock box on ours to the MorRyde one.

step 1 - remove all the stuff attached to the box
step 2 - remove just enough bolts to allow you to prepare to "catch" the box. in my case I let the box pivot straight down and set it on a floor jack, then removed the last 2 bolts.
step 3 - find some way usually with a flor jack and the bed of the truck, to lift the new box in place and start stabbing bolts. Again, I chose floor jack and vertical making up 2 bolts, then rotating in to position (no pictures as it's hard to run a camera while waiting for the box to fall and take out a toe).
step 4 - torque and re torque all of the bolts
step 5 - put everything back on the box that you removed. Typically the break away switch.

As for recommendations on which box, that's all personal preference.