ProDave

It is common here to get a week or 2 at -10 in a winter and we have had no issues with that temperature bothering the MVHR

Just jack up both ends more, yes it will bend the chassis back to being more straight. Ideally you want all the supports to be taking their share of the weight. At the moment it sounds like the centre / axle jacks are taking most of the weight and the end ones are just stopping it tipping up when you all walk to the same end.

I have a different unit but the operation is similar, the bypass flap only diverts one of the flows away from the heat exchanger. But this brings the discussion to looking closely at that mechanism. If the bypass flap is not closing properly when not in bypass mode, it could perhaps be the route of the "leak"?

It probably came from a holiday site where they expect a relatively regular turnover of 'vans and they plug the mains into a socket like touring caravans do. Just ignore it for now. Most likely your electrician will connect the cable direct to the consumer unit in the 'van but he could also just fit a matching socket and just plug that plug into it.

I have an Enthalpy mvhr unit. It was more a case that one was available at the right time at the right price than any technical reason for choosing it. One advantage, not mentioned yet is an Enthalpy mvhr unit does not need a condensate drain, so installation is slightly easier.

Did they check the unit was actually connected correctly? When I installed my unit I found the terms used to describe the ports confusing. Could it be something like the supply vents supplying air to the rooms is mistakenly connected to the exhaust air port that should be exiting the house? I would have expected Brink to have checked this on their visit but perhaps they "assumed" it must be connected correctly?

That was an option I dismissed. It was a flat aluminium roof. Unlike tiles, there is nothing to slot that under. So it would rely entirely on being stuck down with some glue / sealant to keep the whole thing watertight. Any failure in that and it would leak. My swage up the under sized hole forms a natural upstand to divert rainwater around the hole, and I well sealed it as well. I guess I could have then put one of those over the top to make it look better.

Mine is a much more basic 'van with just a plain aluminium roof. Having failed to find any fitting or flashing made for the job I improvised. I cut a hole in the aluminium slightly smaller than the flue, then carefully swaged the edge of the hole upwards until the flue would just fit through. the swaged edge formed a small upstand so water running down the roof would run round it. The hole was cut mid way between the roof joists. In the void I fitted a clamp to retain the flue in place. There was glass wool insulation in the void that was cut back to clear the flue. The inner "ceiling" was hardboard / plywood material. I cut a larger hole in that to maintain the 50mm from the twin wall flue to combustible materials and covered it with a stainless steel closure plate. The kink in the flue as it exits my stove was to align the twin wall with the centre of the gap between joists. The stone the stove sits on and side and back pieces were all offcuts I had collected some time ago to put in the "that will be handy" pile, and they were. It was not possible to maintain correct side and rear "distance to combustibles" so I used stone slabs to protect the adjacent furniture and wall behind the stove, with an air gap left between the wall and the stone. It did a lot of burning and nothing got too hot or singed.

DIY

Yes wiring regs dictate you should not connect a caravan to a TNCS / PME earth system, they should be connected to a TT earth which in simple language means it's own earth rod. The black thing on the wire is a cover to protect the electrical connection clamp at the top of the earth rod.

I fitted a wood burning stove in ours. It hardly went out from November to February and kept us warm through a Highland winter at little cost but it was a lot of work keeping up with the wood to feed it.

Your stove flue should at least continue up into the ceramic flue above the slab and be sealed with a closure plate.

Build internal walls of timber and plasterboard. Then only supporting walls will need proper foundations.

Ditto to above. You want simple and reliable, then old fashioned hard wired light switches like we always had.

On mine the axle is just a tube between the 2 wheels and I lifted on that and put the first two supports under that. It was well balanced on the axle. It is not an officially marked jacking point but it is certainly strong enough. It won't tip up or move because you will have it hooked to your cars towball at that point won't you?