I have a 2012 Georgetown XL 378TS which is the one you also like.
Your initial travel expectations and retirement time was very similar to our.
As you can see in my signature below we are now over 35,000 miles and love the 378 which fits our needs, Gas is the only way to go for being on the road 3 months. The Ford engine chassis and drivetrain is great.
Now the Forest River box you must consider will have problems and you need to make sure you have a dealer that sells the rig is reliable and can handle all warranty quickly. The floor plan in the 378 is amazing as well as the ceiling height. The true paint job outside is great. You need to go up onto the roof before buying and check for any stress or bubbles under the fiberglass sheet. This has happened to many and myself included. So far no further issues so far but I had FR note it under my VIN # as an issue in the future.
Check the hydraulic lines, pump, Leveler jacks for any red hydraulic leaks or bubbles on the lines. This also need to be taken care of immediately.
Get email approval from Forest River first to get frontend checked and aligned ASAP from FORD commercial truck dealer. This need to be done within 90 days of you driving off the lot.
Some of the things I did to my rig.
1. Installed Washer/Dryer combo. Dealer did this to get the sale for $750 which is half the cost of the washer dryer and installed it for free. Wife will love you for it.
2. I removed the bedroom glass door as it got in the way on long trips as well as it must be closed to use the sink.
3. Convection ovens has been a big problem on breaking. I have the true gas stove top and oven.
4. Residential refrigerator is great. Make sure dealer shows you how to turn invertor on as this only runs off the coach batteries then converted to 120 volts AC.
5. Check the rubber seal around the front windshield that it is flush and no gaps or protrusions. Should be smooth and flat all the way around.
6. Pulling a small car behind is no big deal. I have a FIAT that weighs only 2365 lbs and easy to hookup and disconnect.
That's it for now and I'm sure others will add other things.
Have fun and enjoy it is the only way to go.