Yeah it was an Autosleeper www.autosleeper.co.uk the manufacturer of my babay they are a pop top but not in the conventional way it pops up an its sides pop out the only problem with them is price and NO other manufacturer makes such a rroff other than Autosleeper it is ione of teh many reasons i opted for mine [although mine is a high top] Autosleepers generally hold their value well take mine a 1995 Trophy model woth in insurance terms in excess of 12k and to sell about £10k all day long a 60+ year old company here in teh UK making vans that last unlike many today........
For a normal pop top on a T5 you can get a addition called a mutze top i think its called its basically just a thermal top that goes over it made from the same material as the silvver thermal window screens that supposedly keeps the heat in, i know one guy who swears by his and often uses his van in winter as a consequence but you hit the nail on teh head this is why when i last year had a self designed pop top built after only using it twice once in August and once in September i sold it as i had blue Propex [the hotest version] in ours all brand new stuff and i couldnt keep it warm, we had to keep the bed boaards in place to keep any warmth in her which kind of defeated the point of having a pop top and mine was double and treble insulated in places with the remit to kep it as hot as possible. [i shall attempt to source info on cap and get back to you on it]
The UK is NOT OZ my friend heat is not something we are used to be well aware of this