I've walked nearly 80% of it (Devonport to Lachlan). A lot of it is on forestry tracks, farm tracks or just lesser used roads. However, where the book advises bikes to take a detour there is usually an off-road section, sometimes a very rough track or no track (through paddocks). I think you could take a trailer if you use all the recommended detours for bikes. It's an interesting cross-section of Tasmania, through farms, forest (old and new) and bush. The Trail tends to go over a lot of hills to avoid taking sealed roads around the hilly bits.
Check the website. Part of the trail is still closed due to the fire at Lake repulse, but the bikes detour round that area, so it won't matter. The track from Lachlan to Judbury has only just reopened and that's my next section, so can't comment on that.
Some of the downhill sections are reported to be great fun on a bike, but might not be so good at high speed with a trailer. In a few places you might need to heave your bike over fallen trees, but they try to keep it clear enough for non-jumping horses.
A GPS is recommended, since there are some critical checkpoints. However, it is mostly easy to follow with a map and the instructions, with the signs usually there to confirm you are on the right track. The hard to navigate sections where signs are essential are not in the rideable parts. If you get the on-line book they should be able to also supply colour maps that are heaps better than the black and white ones in the book.
ad on an earlier post that it wasn,t. Would a GPS be advisable and does the book give any co-ordinates. 
