Just started our 2nd/new solar install... 2015 Flying Cloud 25RB. Renogy 400w kit, MPPT charge controller.
Previous experience - installed 200w of panels onto 2004 Classic, had to 'create' my own external to internal wiring path (above fridge)... we've been able to boondock 2-3 days with 200w solar and some generator augmentation just because.
+/- "determine your power consumption"/battery use/management assessment... if you have LED lighting, the furnace fan is the most significant power hog - 4 amps draw cycling intermittently. Next may be the water pump.
Can't yet justify $1000-2000 of lithium batteries. ~$200 every three years is not un-manageable budget-wise.
If your model is pre-wired for solar, great... our 2004 Classic 'sort-of' was - 'solar' tagged wires behind the fridge. 12ga wire hard to find where it went... just enough to handle the 200w panels. A 'telephone tech' set of sender and probe helps a lot. More recent 10 ga wiring should be more than enough to support 200-400w of panels... 15A current flow to the charge controller.
MPPT charge controller - more efficient and 'smarter' about handling different battery types - flooded/water maintenance, sealed, AGM...
The most tentative challenge is location of panels, how to fasten, drilling and sealing the holes. For the prior and current new installation I opted for well-nuts. 1/2" holes, 1/4-20 bolts, ample application of Parbond sealant.
Current install I "opted for"/had to space/position two panels aft, two panels forward to retain decent access to the A/C hump, not have panels protruding forward of the aerodynamic front face/curve, etc.
Little or not risk of punching through to the interior ceiling given the 2-4" gaps between roof and interior. You'll either drill cleanly into skin-only or might encounter an underlying aluminum frame strut.
A step drill bit is a very practical, appropriate tool for the holes... little/no 'grab', paint marked the diameter a step above 1/2" to limit depth.
Ample application of parbond sealant to set the well-nuts, add seal atop them and around the bolts/washers.
May need more "solar wire" than came with the Renogy kit to connect everything. Ordered some addition connectors in anticipation of connecting various panel separations, etc. to all 4 panels in parallel before the junction of panels to pre-wire.
Not done yet... but panels mechanically sound, just need to establish the external wiring harness configuration.
The biggest challenge is that Airstreams design/optimal manufacturing processes totally buries/obstructs access to the battery + and - bus connections under the seating platform. Insane. Going to have to remove several to be determined screws and lift the seating frame/cabinet out of the way to gain proper access (unless I can hire some magical elves to crawl in there...) It's wholly unacceptable to 'intentionally' block access to this critical power system and the 7-wire junction by building furniture over/around them.
More to follow... but bottom-line... 100-200w of solar is more than enough to maintain batteries for storage, and some light boon-docking. For serious boon-docking you'll probably want 400w. And, understand that panels are really ~95% efficient under the best solar conditions. Charge controllers are ~95% efficient. +/- that, Honda generator backup and/or bring along 1-2 spare batteries and fit a 75-150 Amp Anderson PowerPole jumper to connect them in.
Pics of the in-process install: