Without knowing more I can't say for sure that a Progressive Dynamics unit will solve the problem.. Could be a down-line short that is takign out the WFFCO boxes, but .....
The PDI is much better built and should be able to withstand that.
ALSO. Do you plug it in at home? IF so check the outlet. I will describe two common problems one of which I had.. thankfully BEFORE I got the RV.
Many folks hire someone to install a 30 amp outlet, the electrician looks at the TT-30, completly fails to notice where it says 125 volts and wires it up for 240, You see, he mistakes it for a dryer, Air compressor, welder or the like outlet. Thus frying your converter (And a bunch of other stuff). I did not have this problem when I installed my 30 amp outlet because.. Well. *I* Installed it.. personally.
The other, which I had fixed professionally, is an open neutral (You see it was not my problem it was Detroit Edison's since it was before the meter).
When my window A/C kicked in what it did to the leg voltages in my house was.. Amazing,, One side went up to over 150 volts while the other dropped to less than 90.
That kind of voltage can also fry 'em. You will note the two voltages i mentioned add up to 240, Just the neutral was not where it belongs.
Home is where I park it!