If I’m reading you right you want to get well off the pavement on FS roads. That’s been my style of camping forever and I think you’ll have to sacrifice a lot of space to do that. Tents, a PU, a PU truck camper or a small TT, maybe 20’ or less, work best for that. A FW is simply too high to get down heavily forested roads though they would work OK at lower elevations with sparse trees.
I camped for many years with a tent and camped anywhere I pleased. Then a got a PU and used it for many more years. It wouldn’t go everywhere I took my tent, but it would get pretty far back in. Then I went to a 16’ TT in 1989 and I’m still using it. It won’t get as far back in as the PU, mostly because of the beating it would take on the roads. But again, I can get pretty far back in, well away from most RV’s. My perception is that once you get over 20’ you start having limitations on where you can go and at 25’ the limitations would be far more than I’d find acceptable.
I’m reminded of a saying my dad used on me when I was a kid, “You can’t have your cake and eat it too”. Likewise, everything with an RV is a compromise. If you want comfort and amenities you sacrifice the ability to negotiate the more primitive roads and camp spots. If the more pristine country is more important you have to sacrifice the space and amenities. It’s up to you to find a balance that suits you.