Be very very careful about who you choose to do the conversion, sooooooo many cowboys out there and some well known names are amongst the cowboys.
Oil filled rad in the awning and in the van works pretty well and won't trip out the electrics at 2 in the morning.
The poptop will be cold and will let cold air down into the van, you can insulate them relatively cheaply though, there's a thread on here somewhere.
When I had my van converted in early 2018 we camped out from April until September, we had blazing sun on every trip, probably 6 or 7 trips that year.
2019 has been the polar opposite, it's been cold and wet on every single trip we've made this year, in fact it's been so bad that we've cut every single camping trip short due to the wind and rain.
If I had the same opportunities again I wouldn't have bothered with the conversion and would have sunk my money into a caravan, which is what I ended up doing in September.
We had a lovely warm/cosy few days at Longleat this weekend, the wind and rain didn't affect us at all.
£10k gets a decent caravan, just saying