Well, first you're gonna have to define "shakes" a bit better.
If you want it to feel like you're walking around you house you might as well give it up now.
If you've got a couple 200-300 pounders stomping around inside, same deal. It's gonna move.
Truth is, it's a trailer and it's gonna move some.
I'd say if you have the stabs out, xchocks in and leveler blocks down, it's probably as stable as you're gonna get it short of reinfocing the frame, floor and several hydrulic levers.
One thing you could try though:
Put a jack (trailer stab jack) just in front of (or behind) the main wheels on each side. Just load the frame (the actual frame, not the body) a small amount. What you're doing is taking the weight off the springs that the middle of the trailer is supported by and solid mounting it. It will remove a fair bit of "bounce".
Other than that, just enjoy being in the trailer away from it all....it's all part of the experience...
2011 Flagstaff Classic Superlight 831RLBSS "Atrium slide"
Husky Centerline Hitch
1998 GMC Sierra SLE K2500 6.5 Turbo Diesel