When applying the re-proofing stuff, pop the tin into a bowl of hot water which softens/liquifies the wax and makes it easier to apply. Keep topping up with hot water as you go. Use a soft cloth to apply wax to the jacket, working in small overlapping squares of 10 cm or 4". It's fiddly and tedious but does a good job.
My Northumbria jacket is 20 years old, stands up by itself and is totally waterproof. It's been back to the factory twice, once for a new zip and once for a replacement panel where I fell through a hedge when duck shooting and ripped a large hole in the back. Each time it came back re-proofed, at no extra cost.
I know waxed cotton is old technology in these breathable, Gore-Tex days but I just can't bring myself to dump it