To avoid building any frame forward of the rear axle to mount trailing swing arms you could modify the rear cargo carrying part to mount leading swing arms instead. With the swing arm pivot to the rear of the wheel you generally want a more solid pivot to handle forces trying to move the wheel sideways (a bottom bracket ought to be ideal) and you want the pivot slightly lower than the wheel axle to encourage the wheel upwards on hitting a bump. Without this you're trying to force the wheel into whatever it hits. This has the advantage of the chassis doubling as the cargo area floor thus saving weight. The shocks would still be mounted at the wheel axle or could be moved towards the pivot as needed. If you use the ex i-lean with a piece of anti-roll bar you could also use that in a leading rather than trailing set-up.