I've got a unconverted (well, mid conversion!) LWB HiRoof Transit Van which I've been gradually insulating whilst using over the past year.
I've used 2 layers of camping mats, then carpet for the floor and can walk around in socks without feet feeling cold. In the winter I use a big piece of lino (found in a skip
) and / or clear plastic mat (£4 for a 6ft runner from B&M Bargains) on the floor to help protect the carpet which of course adds an extra layer of insulation.
On the roof I've used silver bubble wrap loft insulation (around £12-£15 per roll, cheapest place I've found it is Wickes, buy plenty now as it's difficult to get during the summer, and you might pick it up a bit cheaper in a few weeks time when the DIY superstores sell off winter stuff) which was glued straight onto metal using spray glue (£1 per can in pound shop). I've then put a layer of camping mat on top of that. From what people have said I should have probably glued the camping mat to the roof first and then put the silver bubble wrap onto the camping mat, but I'm planning another layer of silver bubble wrap on the roof anyway.
The cavities in the roof ribs were stuffed with whatever scraps of insulation I could find - off cuts of camping mats, silver bubble wrap, foam rubber, and I've got a few cans of spray insulation for those hard to reach gaps when I've completely finished the insulation.
The cavities in the doors were filled with sheep fleece - I live in a rural area and know a few farmers who have been more than happy to donate a few fleeces as they only get about £1 per fleece from the Wool Board and they end up burning alot of fleece which the Wool Board doesn't want. The fleece is filthy, stinks and is full of lanolin but I wash it in the washing machine in a pillow case (only wash a bit at a time) usually several times with a final rinse in vinegar and it comes out slightly felted, and when dry, there is no smell. I've also used either camping mat or silver bubble wrap on the back of the ply lining for the doors - not completely vapour proof but it should do the job. If you don't have a friendly farmer, you can pick up rock wool cheap in a few weeks time when the DIY superstores sell it off cheap in the spring sale.
I'm just about to remove the side ply linings in the van and insulate behind them the same way as I have done for the doors.
Any bits of bare metal are covered in aluminium tape - I found a supplier on ebay which does it for 99p per roll and bought about 5 rolls. Occasionally you can find it in pound shops. Eventually I'd like to completely carpet the sides, roof and doors but I need to wait for a win at bingo for that.
Total cost (like you I'm on a very low budget) has been 4 rolls of silver bubble wrap = approx £50, about £15 for spray glue and aluminium tape, about £10 for camping mats (I got a few for £1 each in the end of summer sale at B&M bargains and I already had 3 or 4 from my tent camping days), the cost of doing about 10 washes of fleece with vinegar (under £10 probably), a couple of rolls of duck tape (£1 each from pound shop). Can't think of any other expenses. But it's been a time consuming process and a labour of love, so although costing more, Kingspan is probably much quicker and easier to use.
I have a whirly bird roof vent which I always keep open no matter how cold it is. The first time I ever slept in the Transit, it rained constantly for the 2 days and nights and I woke up to a waterfall of condensation. Now there is virtually no condensation except for on the coldest nights or in the wettest weather when I get a faint misting on the ceiling. Hopefully another layer of silver bubble wrap will eliminate that.
Interestingly I spent 3 nights in it during the snowy weather a couple of weeks ago, and when I woke up in the morning, I was warm as toast but the top side of the blanket on my duvet was quite damp with condensation. But there was virtually no condensation on the roof.
I will be putting extra insulation on the roof above the high shelf and above my "wardrobe" as I've noticed that if there is any condensation that's where it tends to be, presumably because the air can't circulate as freely.
Draught proofing is as important as insulation in my opinion especially for a conversion - there are strong draughts from the bottom and the join of the rear doors, and along the bottom of the side sliding door, so good old fashioned curtains and draught excluders help stop those. The curtain to the cab has recently been lined (using spray glue and some not very neat hand stitching) with silver bubble wrap and that has made a huge difference in keeping heat in.
I'm planning eventually to do some insulation in the cab too, behind the door panels and on the floor etc. I've made myself some "made to measure" internal window screens, again from silver bubble wrap and window suction hooks (about £1 for a packet of about a dozen at Christmas time) which I use at meets or "safe" wilding spots, campsites etc. They also make a massive difference.
It would be really interesting to get an infra red light on the van and see where the worst heat escape comes from. Probably through the roof vent but for condensation and safety that has to stay open.
