If I were doubling, i would probably use a lighter weight shock. Its about weight and rate, the monroes for example claim they are for class 7-8 trucks(26-33K and over 33K). by published spec ours are class 6(19-26K) Now IMO it is a grossly overbuilt class 6, but those are the weights...
Now if these shocks were specced for 26-33K+, a pair of them would probably make for a pretty restrictive combined force(make a speed bump feel like hitting a curb), same weight and rate, but now twice the resistance... A pair of lighter weight class shock would give you added valve passage and surface area for heat dissipation without overly restricting the weight trying to move at its normal rate for a given task(like sucking up a speed bump)...
Short of paying a grand plus per shock for something custom for our application, this is where we are.
1. used OEM,s for which we have no spec info on the weights and rates for which they were valved
2. some flavor of truck shocks. if you cross that monroe number you can also find a few other manufacturers with products in that class. I have not had a chance to explore down those paths to see if there is perhaps something better still from one of those other manufacturers.
3. mix and match doubled lighter class(pickup shocks) to find a good rate for our weight. It then becomes a challenge to find shocks with the appropriate length and travel...
4. custom built $$$$$.
Aren't LMTV's fun