I just left mine open. Just more ventilation. Not much can get up there unless you have it in that deep of water or mud. Have heard of people running their lift pump return to it. You could always put one of them rubber vacuum caps on there.
thanks now I have to delete or figure out how to run efi live from my laptop and follow 25 "easy" steps (hope I don't screw anything up) in order to save my previous deleted files and download and install new non-deleted files onto my autoCAL. 
I swapped mine to 140 while back. Helps alot with the truck runs both the grid heater an glowplugs are the same timeChanged the alternator on my truck. It stranded me (battery light been on a few days so I thought the gauge was just bad since it kept starting/running fine & not dipping below the tick halfway btwn 9 & 14V). That procrastination bit me yesterday morning. Not too big a deal though since it was at my house.
Had a 105amp unit on it but I stepped up to the 140amp unit with the replacement. Can't complain about the original unit, it had 195K miles on it unless the original owner had to change it in the first 75k miles. I've put the last 125k miles on it & know this is the first time it's been changed since I've had the truck.
Not a bad job to do but damn it sucked getting the bottom bolt lined up just right. Hell it took an hour to get the bolts back in.
