We have a 2015 2504S for a year now and have made a few changes.
Yes you can fit a foam topper on the mattress with no problem. We have a 2" gel foam topper along with a fitted mattress pad ordered from Amazon. Adding them has made a world of difference. The pillows are stored on one of the bunks during the day.
We did upgrade to an Insignia 32" TV from Best Buy. It is just about the same size as the opening. When the TV is "locked" into place on the TV mount, it sticks out about an inch or so from the opening so it isn't an issue. I did however have to move the TV mount up a few inches to center the TV within the opening. Without doing that the TV sits too low. On top of that, I installed an Insignia sound bar above the TV fastened to the ledge of the counter top at the foot of the top bunk. The length is a perfect fit. I did this since the iRV 33 AM/FM/CD/DVD/MP3/MP4 is defective.
Also, the dining table was shored up with two vertical 1"x3"s bolted to the top and bottom metal frame with angle iron support on both ends of the table fastened to the 1"x3"'s and the table top. Chances are we will never have to use the table for a bed so it is feasible for us. It did take care of the wobble by about 90%.
Lastly, I do remember seeing somewhere complaints about the dining table area cushions. The padding used is not supportive and is very uncomfortable if you sit on them for a period of time. We fixed that by having the cushions re-padded with a more dense foam at a furniture shop in York, PA. A little expensive but worth it.
Have a good day.