LPG Tank replacement

Hi All,
I am trying to replace the lpg fuel tank as the multivalve on the current one appears shot (gauge tells me it is empty but it won't fill.)
It has never worked for me since I've had the van - it didn't come with a filler cap so most likely some crud has gotten in there.
As the tank itself is fairly corroded I thought it was probably best to replace this alongside the valve.  The only supplier of tanks I've found that do them to the same dimensions as the one already on my pickup have asked me which type I have

"Thank you for your mail,
It is no problem to supply the parts you need. Most of these factory fit Hijets had a four hole cylinder tank fitted under the rear. Is yours one of these? - (a four hole tank has a row of four brass valves on a plate as opposed to a single hole which has one round brass valve held in by six allen bolts)"

Now, I think it is probably the single hole variety given the pictures posted by stevelav here
https://hijet.forumotion.com/t1093-unmounting-1-2-full-rusty-lpg-tank
For a van?
The trouble I have is that there is an elongated cup shaped metal plate obscuring the valve and inlets from view and without taking the tank off I don't think I can positively say which of the two it is.
Can anyone help please?

First of all, you sure that your LPG Tank is empty as I have often bought a Hi-Jet showing no LPG lights and the tank has been full. Have you tried tapping the tank with a spanner to see if it sounds empty or full up.. Switch problems could be one of the microfuses on the brain under the passenger seat.

Secondly the Van LPG tank is at the rear under the floor and bumper between the battery box and exhaust tailpipe and is totally different dimensions to the Pickup.

The Pickup as you are aware sits on the Offside, mounted on the chassis rail. It's longer and thinner than the Van tank. Definitely not interchangeable.

Thanks Woodie,
I replaced the fuses when I first looked at the lpg system and they should currently be in good working order as there are lights on the gauge, is there an independent fuse specifically for the solenoid valve?
The whole system was disconnected when I got the van hence my earlier posts regarding plumbing in a new reducer (it appears the diaphragm had failed on the old one as there was coolant in the gas line.)
I am aware that removing the tanks is dicey as even when empty there can be residual gas in them, hence why I have employed the use of a reliable plumber who has experience with lpg.  I tried getting help from an LPG servicing workshop (Causeway 4x4) within reasonable distance of me but after they were initially keen to do the work, advising me that the multivalve had likely got stuck and it was probably worth replacing the tank at the same time, they went cold and didn't return my communications.
I have also taken the van to the guy DorsetLPG in Poole who ran diagnostics - he told me he was the only person left in the country with the diagnostic equipment for these old Prins AFSII system.  The electronic side of things was supposedly functioning correctly.

He was the installer of all the Romahome Hi-Jet systems. If he can't sort it out then I don't know who can.

ah really, the same one you mentioned in an post just a while ago?
He only looked at the electronics side of it and suggested the reducer would need replacing.
Tank issues have been subsequent to that.