I thought I needed to find the current this heater unit draws to fit a thermal switch, and hence was waiting for the high power resister to measure it. But I thought about it a bit and worked out that if I put the relay in or close to the heater box, and put the thermal switch between the ignition fuse and the relay control, I can do it with a low current device. That has the added advantage of saving a couple of bob too.
I'm not having the success I expected in finding more powerful fans than the supposedly 4.5 Watt ones supplied - don't think they blow that hard, though I haven't checked if they are drawing 0.3A as stated and I've a suspicion they are 0.13 fans mislabeled. It's my experience that's a real problem with things with the sort of origin of this box.
But on the replacement fans - if that's what I need -, when I was investigating the idea of putting fans behind the eyeball dash vents (it works, but it's not really worth the effort), I found a 25 Watt 60mm fan out of an IBM server hot-swap module at a reasonable price. That's a real screamer and needs a switched mode controller in series to tame it a bit. But now all I can find are 10W units at anything like a reasonable enough price, and I think I may want more power than that - however much it may corrupt.
There's also a small issue with the vents. The Herald ones I have aren't worth using. While there are some 40mm vents on ebay that should fit the pipes supplied, the ones I like are 42mm ones.
I expect I could join some 42mm pipe to the 40mm (but the 42mm pipe adds to the cost more than I like) or maybe split the 40mm pipe and tape it to fit the 42mm vents. So I'm vacillating about what to buy.
Graham