Beyond disgusting. I'm so sorry you have to deal with this. Mice are beyond persistent and able to get through spaces so small you would shake your head. And, they can chew through just about anything. If they have tunneled through the insulation (and it surely sounds like they have), AND if you push this issue about eliminating any possible residue, you'd probably have to clean out your entire interior, pull the skins, clean out whatever you find that shouldn't be there....and re-rivet. If it were me, I would DEFINITELY drop the belly pan because you ain't seen nothing until you do that. I would leave the interior alone after making sure that all the lights and electrical outlets are solid (no chewing through insulation)....and I'd consider talking to an exterminator about residual effects of mouse manure/urine on your health -- particularly in a closed in space like an A/S.
"SilverLeaf II" 2015 30' Classic
2019 RAM 2500 Limited 4x4 CC w/6.7L Cummins
WBCCI # 3430-Unit 21