One of the best mods going is to add a Fantastic Fan to your trailer if you don't have one.
The last two I have put in have been Fan-Tastic 802251 RV Roof Vent
Note: Scamp 13's you can't just replace the roof vent as it is not a standard 14" RV Vent you have to cut an additional vent hole in the roof.
This is the vent that was on my trailer, note all the added silicone sealer. 
If a vent or window is leaking, you should pull the vent or window and reinstall or replace it properly with butyl tape. A properly done vent or window install with butyl tape won't have any issues for years to come and you won't see any visible sealant mess. If for some reason you feel you need to add sealer on fiberglass use 3M Marine Adhesive Sealant 5200 Fast Cure White, 06535, 1 oz tube (Pack of 1)
Inside after pulling the original vent trim ring. Escape's are pre-wired for fantastic fans which you can see the wires hanging down. If your vent opening is not pre-wired you'll need to fish the wiring from wherever works best.
Vent removed and is setup with screws into wood reinforcements between the roof panels
Cleaned up easily with putty knife and Goof Off FG651 Professional Strength Remover, 4.5-Ounce
Placed Colormetrics Gray Putty Tape / Butyl Tape 1/8" x 1" x 30' (Single Roll)
Cut the trim to correct depth, wired the fan, screwed the trim on and fantastic fan is done.
With the fall weather upon us, can't wait to fire this up in the campground.... 
My vent opening is approximately 14x21 previous owner had replaced the original. Would a fantastic fan fit?
No, that is the downside with the weird dimension escape vent Scamp uses. Standard RV Vents are 14x14 and that is a swap for a fantastic fan. Subject of this post http://www.scampcamper.com/forums/escape-hatch-gone which is so exciting that Scamp will put in a normal vent or fantastic fan instead of the escape hatch when building. Unfortunately, everyone out there without a normal vent opening has to cut an additional hole in the roof to add a fantastic fan.
Our Trailers:
2015 19 Escape
Buying or Selling Molded FG Trailers:
Fiberglass-RV-4Sale
Folks,
I want to adapt a Fantastic Fan to an escape hatch opening. I have a bunch of aluminum 3003 1/8" sheet. My plan is to cut a rectangle of aluminum the size of the escape hatch mounting flange. I'll then transfer the mounting holes to the plate, Then, I'll cut the opening for the Fantastic Fan. The fan will be mounted to the plate before the plate is mounted to the hatch opening. After the adapter is sealed and mounted to the trailer, I think I can add insulation and new wide trim to the installation.
Does the above sound doable?
Bob H.
Bob,
Definitely could be done, but my thoughts are that it won't be rigid enough. I would probably cut a plywood plug that fills the escape hatch hole with the matching fan hole and sandwich that between the exterior and an interior aluminum plate. You could then use SS bolts and nuts through the two plates for both the plate mounting and the new fan mounting. A bit more involved, but would be very solid.
Our Trailers:
2015 19 Escape
Buying or Selling Molded FG Trailers:
Fiberglass-RV-4Sale
Greg,
I was on the topside of the 5er yesterday. The mounting flange on the escape hatch is a serious weldment. I could tig in a frame that would drop into the cavity in the roof. I noticed that there is a gap at the left and right ends of the escape hatch flange. Both hatches had a small leak, so I cut out the sealing caulk and attempted to reseal them. I also have .090" thick aluminum.
I can see how the hatch flange could add some stiffness to the hatch opening. I had removed the old water heater and added an a thin aluminum panel. the fiberglass around the water heater was easily used out of shape with the drill and pop rivet tool. Live and learn.
Bob H.
My rough opening is 14.5" each way. Will this fit and is the weight too much for the roof of my 1983 16' scamp. I expect I will have to add some bracing around the inside, will that make up the 1/2" difference?
Jim and Theresa
Heading out West