I cant find the name but there is a sound/heat liner made for hot rods/ classic cars with big motors/exaust. I know a guy that used it and it was awesome. Search web or summit.
Herculiner bed coat is good. Monstaliner is 2X the cost but not as rough. Your call. Carpet for sound and a liner under it.
Lizard skin, is the one, iirc. Most sound dampening companies sell those products. Most are just over priced elastomer (sp?) paint, the energy saving stuff used on walls facing the sun, rooftops, etc. Often mixed with bags of micro glass bubbles. (sold in hobby shops for model aircraft) Search the web for DIY mixes and save a bundle, those dampening paints will have you $200 into $20 of retail product..
Even then your Jeep will still sound like a box, just one with a lower resonant frequency. If you have a droning exhaust it'll just become more annoying while cruising. To sound "proof" you need to block incoming sounds of all frequencies. This requires several types of sound barriers, in car audio its usually vinyl and open cell foam. The paints and butyl or tar mats, reduce the resonant frequencies, mostly generated by speakers being mounted to/on the car's panels. The paints and mats don't do much to dampen outside noises. Maybe a bit when a 130 db Ti rice can flies by, at least I can hear some vehicles panels vibe when I blast past in my burner.
I had a luxury sedan that was once very quiet, everything (even the center console, glove box, wires wrapped, I mean everything..) was lined with open cell foam. Keep in mind foam will deteriorate and needs to be replaced every 5-10 years of normal use. Or our case every time the Jeep takes a bath in the creek
Btw that vehicle had maybe 6 pieces of mat to knock out the resonant frequencies. Covering the car with butyl mats is just a wasted weekend, hundreds $ burnt, and a couple hundred more on the springs.
Edit: If I didn't like the noise, I'd start with a headliner first. That will probably have the single largest impact of your deadening project. < Assuming you've kept/put carpet back in. Otherwise its a toss between the two, depending on top (soft/hard) and the frequencies of the noises.