I recommend using the Stromberg Carlson Base Pad Peak # SC58MR for the scissor jacks on your 2008 Fleetwood Mallard. Currently Snap Pad does not manufacture pads for your scissor jacks. The Stromberg pads are 8" tall reducing the amount of the jack that must be extended. view full answer...
I've attached a photo that shows a similar trailer that a customer sent in that has the same issue and has used the etrailer Electric Jack # EJ-3520-BBX successfully. The rear of the head on the jack only sticks out around 1-1/2" from the tube (it sticks out much more prominently in the front- roughly 4-1/2"), so it will butt right up against the propane tank cover, but it will fit.
Even though it is a 3500-lbs jack and your trailer is only 4000-lbs, it's not really over kill and I definitely... view full answer...