Let's compare notes.
Your skylight and mine are different sizes. You "might" have the smaller shower. In the models years of yours, mine and maybe all the way to the 2007's they had at least 2 size showers.
My 2004 T310SR and my 2004 T2499 had the bigger shower. 36 x 23 1/2"
I know the 2005 T280SR and the 2007 T286SR had the smaller shower. I think it might be the 30 x 23 1/2"
What is your shower size?
I have Eternabonded my shower dome outside flange so right now I cannot get to the outer flange, but I can get the inside.
My inside wood opening size and the inside bubble size is 22 1/4" x 14 3/4" x a 4 1/4" inside high bubble size from the mounting surface.
From my research the outside flange "might" be 1 1/2" wide on the sides.
If it is, then the outside flange would be 25 1/4" x 17 3/4" as opposed to your 18.25x16.25.
Here are the places I have found. There seem to be 2 types of plastic, Polycarbonate (Lexan) or acrylic (Plexiglas). By the way mine cracked I'm guessing mine is acrylic. However Polycarbonate has been known to have spider cracks around too tight of a screw or bolts. And a running long crack in is more prone to acrylic than polycarbonate as a general statement from my plastics background.
- This place sells polycarbonate domes that come close to my size. I do not know if the 1/4" increments fall into the next even nominal size. May have to call them. The white one are warranted for 5 years against UV which is the only warranty I have found. However the bubble height is less. For me I would be looking at an inside bubble size of theirs as a 15 x 22 x 3 high against my 22 1/4" x 14 3/4" x a 4 1/4" high
- Here is another place. These are polycarbonate. The outer flange is a little bigger, maybe, the inside a little less, the height is taller. Cost is close to 2x. They include a tube a urethane caulk that has to be used.
Skylights - Replacement Domes
14 x 22 White Outer Dome SL1422W
Rough Hole Opening Size- 14" x 22"
Flange-Flange Size- 17.5" x 25.5"
Double Dome, order part # N1422D
This one is taller and a a little smaller inside
As opposed to my 22 1/4" x 14 3/4" x a 4 1/4" inside high bubble size.
brand. These are polycarbonate and come in sizes like the Pellendant. They also include a tube of caulk.
BRI-RUS Specialty Recreation
They can be bought here as one place. Price is not that bad and shipping may be cheaper. They seem to be on sale now.
RV Replacement Skylights from Bri-Rus - PPL Motor Homes
- These guys state they will custom make every one. Do not know what the materiel is.
RV Skylights, Replacement Domes for RV's - AIA Skylights
- This factory is in Canada. I have bought my AC shroud from them. They have polycarbonate and the company has good quality. Does not say about the caulk we need to use. And they seem to have the size that will fit mine just not the exact 1/4" size. The height is right. The price is in line. Freight, there is no issue importing, they handle all that, shows up Fed Ex if I recall right. They did not list a warranty, they did on my AC shroud which was a lifetime.
Skylights | Sky light Domes | RV Skylight Replacements
For me they offer a
RV Skylight | Roof Dome | SL1422
Fits all standard 14” x 22” skylight openings.
- Dome Dimension: 14" x 22" x 4"
- Outer Dimension: 18" x 26"
As opposed to my 22 1/4" x 14 3/4" x a 4 1/4" inside dims and height of bubble size. While the inside is a little less on the 14" the outside seems to make up for it.
What I do not know is what is industry standard on the size? I'm measuring 1/4 inches which may be inside the nominal size. The outer flanges seem to range from 1.5 inches to 2". The need is the outer flange has good coverage to create the seal. If the inside is a little smaller will not affect the operation. As far as warranty I have only found the one place that states what it is. Polycarbonate when bought on the vent hatches comes with a better warranty than the acrylic from what I have found.
I will have to research or call about the sealant to make sure it is compatible with the rubber roof and the dome plastics. Before researching this where some come with a urethane sealant, I was thinking they used butyl sealing tape. But maybe not. Have to find that out.
Hope this helps. Let us know how you make out. I will pass along anything I hear. I will try to start calling places this week.