Still a fairly new Heartland Trail Runner owner, since we took delivery of our 302SLE at the beginning of August. But I have made a few, what I consider, improvements.
The first, and best in my wife's opinion, was to replace the tanked water heater with a tankless unit. The only problem was that the door, which you have to order separately, for the Girard Unit only comes in white. Well, the color scheme of our Trail Runner is black, so I had to scuff up the factory finish with 0 steel wool and repaint it black. I did mask off the latch and left the silicone ring white for accent.
Secondly, I rerouted the refrigerator defrost drain hose out the bottom vent openings on the outside refrigerator door. It's no longer just balled up inside the compartment. I did this when I installed the Camco bug screens on the door. I also installed the Camco bug screen on the furnace opening.
Thirdly, I added a bracket behind the spare tire rack to allow storage and safe traveling of a fold-up ramp. The ramp is to allow our older dog to get up into the truck bed without difficulty. I'm a wood worker, so it's a homemade ramp that's 8 feet long and 15 inches wide. It folds up to make 2, 4 foot parts, that are both stiffened when in use and kept from opening by 2 pieces of 1 1/8 in wood dowels fed through conduit straps. The whole thing, including the bracket was far less that shorter, less sturdy ramps that are commercially available. The total cost was less than $40.00, which was about $20 cheaper too.
Fourth, we used the space in the entertainment center to mount a 32 in smart TV. We took advantage of the fact that the entertainment center shares the wall with the bedroom by drilling completely through the wall for the top bolts of the living area TV mount and the bottom bolts for the bedroom TV Mount. This worked out very well when coupled with stabilization straps to minimize the vibration during travel.