We bought the A122 a year ago. With 2 kids in college and a visiting mother-in-law, we learned the value of the foam toppers. One night in the camper convinced us that a foam topper was needed there, too. We generally buy ours from Costco - size is an extra-long full. Now we sleep well at night.
Don't know how well the heated mattress works through the topper - we have never tried it. Set the heater to 55-58, and with a light blanket/cover we stay plenty warm on the cold nights.
The topper makes it a little more awkward to lift the bed to access the space underneath. But we generally only store stuff we get out at the beginning of the trip, and put back at the end. Things like the gray water bucket and hose, camp stove, propane lantern - items that are too big or too far forward to get out the rear outside door, but are only accessed once per campsite.
At the right rear door, I have chocks, my stack of Lynx Levelers, level, tongue jack wheel, equalizer bar lever (never used), lug nut cross (also never used yet), electrical cable, water hose. These are all things I use in setting up the camper (or repairing), so I have them accessible from the outside. Tools, 1lb propane cylinders, and similar are in the left side rear with the slide out tray.
Dry food, cooking and dining gear go under the dinette seat - to which I added a latch to hold open.
We made the deliberate choice to buy the smallest A-frame for an easy fit in the garage, and have it pre-stocked for our minimalist camping. Toss 2 smallish coolers with food and drink, the EZ-up for the picnic table, and a small duffel each for clothes in the minivan, and we are ready for a weekend trip. Plug in the camper, pre-cool the fridge the night before (and recharge batteries), load the van, hook-up, and go.
just our experiences
2014 Rockwood A122
2008 Hyundai Entourage with Equalizer 600/6000 WDH and anti-sway
camping Colorado (and Nebraska, Wyoming, Utah, Texas, New Mexico) one weekend (long or short) at a time