Shocks that work correctly will be very difficlt to install. I looked into installing them on our 343RL and the angle instead of being near verticle are at something like 30 degrees off of HORIZONTAL. There is a company that claims to have solved that angle, and there are some You Tube videos that shows the installation. I'm a bit skeptical but it is worth a look :
If your HC has the MORryde CRE 3000, you can upgrade to one of their higher levels. You might also consider uprating the suspension to 8K by changing springs. That 42 foot RV starts out at about 13K and has a GVW of close to 16K so there is a lot of lever action to wiggle that weight.
Of course IS would be the optimum but is not an inexpensive mod