Thanks for the replies will look at all options at the moment, but cost is a major consideration so although i would love a Nuvinci 380 or 330 they tend to cost more than what i plan on spending for the whole trike especially in Australia as shipping costs from overseas can add up. Still not totally happy with having a belt drive system from the outside casing of the IGH to the rear axle. I By far the cheapest solution is to mount 2 derailleurs (one for each wheel) on the rear axle and this will give me a greater gear change ratio as well - still looking at options.
My terrain is not flat and as I plan on taking it off road I will want some fairly low speed ratios.
Thank once again