As I have built plenty of stuff in the past, I can totally relate to them as to the time it takes to do the fiddly jobs. Like he was saying on the video, it's a case of the 20 minute looking jobs do take 4 hours. There are a lot of little things that take lots of time and unfortunately they are having to do all those little things now which make it look like they don't seem to be progressing as well as previously.
This is just as an extra to a day job. I'm pretty sure they both have families too, and I think Richard doesn't live anywhere near where it's being built.
These things take (lots of spare) time which may be they don't always have due to life getting in the way so unfortunately we have to wait the fair few months in between episodes.
It was bad enough trying to just build the rally car which is relatively simple in comparison without having to think and plan what to film, then edit it all together and stick it on YouTube.