Anyone any good or bad experience of mounting the fuel filler on the top of the rear tub (horizontal surface). My concern would be if I got caught in the rain, how well sealed are these filler caps and what is the chance of getting water in the fuel tank?

Fuel filler is this one;

Mines on the top (a Fury so it has to be). Never had trouble with water in the fuel and I've been in more than a few biblical downpours. Guess it depends on the actual cap design. Mines one of these...
https://www.europaspares.com/exterior-parts/fuel-caps/aero-cap-2-25-flanged-funnel-for-2-hose.html

I do know quite a few people with fillers on the rear panel of sevens and they all have trouble getting fuel in.

On my 7, I have the fuel filler on the sied, i end up with more fuel on my shoes than in the tank, i too have just bought one of these and will be mounting it on the top!

My first build was on the vertical back, a real pain to fill.
This build it is on the top, much easier to fill

DiNoc 3

On my MK Indy I positioned the screw on filler cap below the hinged/locking boot panel. The first couple of fill ups took some care to avoid spills, but after that it was easy. Car got caught in the rain a couple of times and no problems - the filler was below the boot lid.

Both my Strikers have/ are on the top and never had a problem even in torrential rain, also much easier to fill even from cans when topping up on track days

My Haynes used the standard MX5 filler pipe mounted on the flat top of the boot. I have used an ebay locking fuel cap with it and no issues at all. My tank is 8.5 gallons and even when full with determined cornering or in the heaviest rain no issues at all - except I get very very wet that is

Thanks all, will be mounting it on top of my rear tub

thanks for your help, here is the end result with it fitted to rear tub cover and hooked up to fuel tank.

The filler cap is IVA ok with key not removable and fuel hose is certified for petrol use with certificate.

Mine is on the rear panel, and ive often thought about putting it on the top, as filling is a real pita, and I seem to overfill which leaves a horrible mess on the polished alloy rear skin

steve