If the specs are checked the JR Products 541-B-3-A is :
- Cutout Dim: 3-1/2Ē
- Outside Dim: 5-1/8Ē
- Collar Depth: 1-1/2Ē
The Hatches are typically around 4" Dia. minimum, and upwards.
Specs for a 4" Seaflo are :
External Diameter: 5.6″
Opening Diameter: 4.0″
Cut Out Diameter: 4.5″
I believe, that the 4" are probably typical for most applications in our RV storage, with some exceptions like the sewer line. I know they increased the size of mine for the sewer line, as the alignment was quite a bit off and a pain to hook up even the cheap thin hose.
I don't see the extra 1.5" being a big issue. I'm sure I will use the electric cable hatch when I get around to it. After all, it is what used to be used in most RV's. And yes, it's much more critter proof.