On the sidewall fridge vent, I just used fiberglass screen, like you would put on a screen door. You do have to remove it to install, which is only 2 twist lock outfits. Not sure what they are called. I trim and hot glue the screen on the backside of it. From the outside, you don't even see it. It works well and is cheap. On the roof, not hard but a little more in depth. There are 4 screws that secure the vent cap on the roof fridge vent. You'll have to take a small screw driver or something and dig the sealant out of the 4 holes a little. Then just use a Robertson / square drive tool to remove the 4 screws. Once the cap is off, I just took aluminum screen with a finer mesh, like a screen door, trimmed it to fit, and again hot glued it around the perimeter. Then of course reinstall the cap with the 4 screws and fill the holes with self leveling sealant, or what ever you want. I use Dicor 501 for that application, just because it's easy to remove later. Hope this helps. I'll be home later this week from offshore and would be happy to post a picture if necessary. We no longer use our vent panel on the back of the fridge and have a CNC'd aluminum panel in its place. I installed a residential fridge, so no need for the back to be open really. I kept the vented panel just in case.
John and Rebecca Dickson
Emma-8 / Little John-5 / Iva-1+
2013 Ford F-350 Lariat FX4, CC LB PSD, DRW
2015 Jayco Jay Flight 28BHBE (#8)