Have to agree with dg-Cleaning, The only thing I do different is I dont use any Caustic (personaly I think it is nasty stuff and to aggresive) and I use a heated Stainless soak tank, This I find really does speed up the process. I can clean a bad oven in around 1 1/2 - 2 hours.. Basically when using a tank I strip the oven down of all removable parts and put these in the tank, then clean the oven box. The Tank will remove 99% off all burnt on carbon, All I have to do is give everything a quick scrub and a rinse in a rinse tank and all the removable parts are done.
It has taken me a long time and a lot of research to get the right chemicals and the right process.
With regards to a tank well I found they are like Rocking Horse sh*** . So I went to a Fabricator and worked with him and together we came up with a sealable portable heated soak tank for the back of the van. Just have a chat with your local Fabricator, Make sure he is a good one though and dont let them fob you off into using Galvanised Steel, It has to be a good quality Stainless, cost loads more but you will have a tank for life.....
Hope this has helped a bit
Regards Duncan