Howdy and welcome to the forum,
We have a 23RB and have faced similar issues and mods.
1. Intransit, we leave the vent open. Storage in 80-90% humidity, nope.
2. Yes, Frig on Gas is fine enroute. Be sure to watch for the SOLID light, you may have to prime the frig by lighting a stove burner if FLASHING.
3. I'll list the mods on my 20 month old unit below.
4. Extended warranty - It's an insurance policy. IF you service the unit annually, pack bearings ever 24 months, and maintain tire pressure, in my opinion, it's not needed.
5. Depends on the size of the solar panel (mine is 5 watts/ too small) and whether it's covered storage. I have both. My trailer gets the afternoon sun and the solar panel will keep the battery alive for a week. Just installed a Marinco battery cutoff switch on the back of the battery box, for longer storage. If most of your camping is off the power grid, a lot of folks go with 2 batteries. We seldom camp without power, so a dead battery isn't really a problem.
Upgrades and mods:
1. Maxxair vent cover
2. Screen door bar
3. Door sun shield
4. Storage hooks for: the leveler crank, jack crank, TV cable, etc.
5. Digital thermostat, from Amazon Warehouse Deal - Saves $
6. TV mount - called Jayco, they emailed the framing diagram. Still use a stud finder, I have trust issues.
7. Bath tub splash guards. Oh sure, we always are level...
8. Winegard RV Wing Ant. booster from Amazon Warehouse Deal - Saves $
9. Winegard Sensapro digital TV amp from Amazon Warehouse Deal - Saves $
10. Camco 30 amp plug with handle
11. 22" step covers/carpet x 2
12. Camco stove cover from Amazon Warehouse Deal
13. Camco wheel chocks
14. Camco leveling blocks/lego style
15. Camco sidewinder hose support
16. Camco dual flush with valves
17. Added panel to separate the bed from storage - 1"x2" furring strips and 1/4" ply.
18. Good Sam Roadside Assistance (covers RV, tow vehicle, all cars in household)
To Do:
1. Speakers
2. Vent fan
3. Valterra Dominator sewer kit (waiting for a sale)
4. Furrion 30 twist cord kit or Marinco 30 Parkpower kit (waiting for a sale)
This is our 4th RV. Two Jayco popups and a 19' Funfinder prior to this 23RB. We will keep it for 2 more years and decide if we upgrade or go to a motorhome. I am retired Army and really want to see America. Sandy places without a beach, not so much.