This should really be titled as how to fit 5ft 10" & 200lbs upside down into a Sonex. If you suffer from claustrophobia don't read this! In order to fit the tank I thought that I had better get the rudder cables in first as I couldn't see how you could fit in there after the tank is in position. It turns out if there is a will then there is a way. The only problem I ran into was that the length of the teflon tubing I used on the rudder cables was about 1/2" too long and restricted the amount of rudder travel.
This is showing the cables hooked up to my modified tail wheel bracket that has increased the ground clearance slightly.
Now the fun part. ....fitting the tank straps just sucks. It involves climbing in and out numerous times and lots of inappropriate language! You really need to stick your head under there to appreciate what a bugger it is. The last photo shows the fuel line partly completed as I'm gently forming the curves down to the fuel gascolator.