Did it last year, no issues whatsoever.
I have copied & posted below some threads I placed at the time, if they look like they are answering questions you haven't asked that is why!
1st Reply.
Just had mine done, no problems whatsoever regarding distortion.
I bolted a bar across the bottom and yes, the flat panels did ripple in places but now it is all bolted back together none of it is noticeable. I drilled extra holes in places where they aren't noticable and maybe this helped? I cut the mesh out prior to galvanising and bonded it back in afterwards. Taping the holes doesn't take long but when it came to the nylon inserts I decided to trim the insert rather than filing away the zinc and risk exposing bare metal. Some people suggest filing the holes out first and then letting them fill back up again with zinc, would probably work but you could end up with some sloppy fits? I also took lots of photos and measured where the smaller holes were as they can be tricky to spot when full of zinc.
My bulkhead was new in 2000 and I properly Waxoyled it at the time so when I came to remove it from the vehicle earlier this year the only evidence of corrosion was on the O/S inner-wing bracket.
I had 20-items cleaned & dipped including the bulkhead, battery-box, rock-sliders, door-sills and assorted brackets. Including collection & delivery (I am 50-miles from the galvanisers) the total invoice was £144 inc VAT so not expensive.
I am a real fan of Waxoyl so even though it has been galvanised I still filled it full of the stuff before fitting for no other reason than I could (turn it upside down, tape up all the holes and poor the stuff in). I completed the rebuild this weekend and with the recent heat I am just starting to collect the excess Waxoyl as it drips out.
I didn't have mine painted as by the time the doors, wings, windscreen frame, vent-flaps etc are fitted it doesn't look out of place and it also matches the capping (which I had galvanised a couple of years ago). A nice pair of billet windscreen brackets in silver look nice though, better than the painted ones which I fitted and then immediately removed! Might do the door-hinges as well?
2nd Reply.
Don't forget that Ashtree bulkheads aren't brand new anyway, pedantic I know but to quote their own website they are "essentially salvageable bulkheads in need of refurbishment". That said, it is probably the easiest way of getting a good / refurbished galvanised bulkhead with the minimum of work but alternatively you have the likes of Andover Land Rover International as well as other suppliers who supply the same thing.
Personally I went down the DIY galvanised route earlier this year.
My bulkhead was in perfect condition so ideal for the work (if there is internal corrosion the you are wasting your time). The stripping & galvanising operation was very cheap and I suffered no distortion apart from some slight rippling to some flat panels which can't be seen when assembled anyway. I had to clean up the threads (something which the likes of Ashtree do for you) but is very easy and only took an hour or so. Don't forget to remove the mesh flyscreens before dipping otherwise your vents will be blocked (I cut the welds and then bonded the screens in place afterwards).
At the end of the day it is up to you however I really do recommened the galvanising option, how you get it done is up to you. If you can weld and are certain the bulkhead is structurally sound then do it DIY, if you can't weld however just go for a ready made solution.
3rd Reply.
One thing I did mention in the other thread is about the additional holes I drilled. I am now convinced they helped as it meant that whatever way the bulkhead was dipped there was always going to be a way for the air to escape, acording to the galvanisers that is more important than over the top bracing when it comes to items such as bulkheads (they had done a few and never had any problems).
By the way, if anyone wanted the bracing bar shown in the photo bolted across the bottom it is available.
I used East Anglian Galvanising in Sawtry (Cambs) but cost wise I should imagine they will all be much the same. I expect the biggest difference would be if you involve a third party who wants their cut or if they have a minimum charge (EAG doesn't).
With regards to capping etc (mentioned earlier in the thread) I had all mine done plus several other parts (swing away carrier, rear bumperettes, tailgate liner etc) and it all came to under £40 inc prep & VAT. In no way can galvanising be classed as an expensive solution!
