I am currently using 2kg of molasses (food grade black strap) and 5kg of sugar. This is then oaked on heavy toast chips from my brew store. I even tried some caramel, which I found very unsuccessful
Current Fixes I know of are
a) use all molasses (but I know of brands that make heavy rums from cane syrup...so a little sugar in the mix shouldn't stop me from making a heavy rum)
b) backset (some people claim that simply fermenting and distilling molasses isn't a true rum that there needs to be a souring process, like UJSM. However all the distilleries sites I've read through never mention it)
c) Delve deeper into the tails. However my tails taste like crap and don't seem to add any rummy flavor, only "sharpness." Some one has also mentioned that some of rums flavor may come from deep tails...
d)Use Chared oak (As soon as I find some I'll char it and use it, I might try cedar which is plentiful here)
e)Some people have talked about diluting there rum with backset, but either I missed the response or there was none (not worth writing about?)
If any one has hints or positive or negative experience with any or all of these ideas it would be great