Yes while I did some minor stuff with Fumaric Acid, what made me believe is dissolves pretty bad, I heated it to boiling of course ;D

Still I haven't done it with the desired amount I talk about.

Well so in case that uncertainty is caused because of excessive Fumaric Acid -> I would only use the correct amount.

Then one may argue I don't know whether the reaction is complete, but as I said I would just let it stirr for 1 hour or maybe even 2.

And just by thoughts: If the Fumaric acids dissolves slowly (I guess you don't need 20 minutes to dissolve all your stuff), then it will still dissolve permanently and crash out. So this will be a constant process. I would really not consider that it is that slow that I cannot just stirr it for 2 hours and then it wouldn't be complete.

But yes: I WILL try both methods ;D

I may test if the other method just yields Fumaric Salt + still free Fumaric Acid if I can dissolve some back with Naphtha (which would dissolve the free DMT) and then the weight would be lower.