i have almost the same trailer setup, except my harbor freight trailer is a 20 year old pos lol.
how you have it is pretty much fine, but as other's have said i'd invest (<$10) in soft straps that go around your handlebars. especially with this trailer, i'm a huge fan of straps that fully go around the tie down point. here is an example. so if you go over any bumps and your shocks compress, there's no chance of the straps falling out of the tiedown points. straps like that have given me tons of piece of mind.
I just had an idea. What if you combined pillows, cushions, blankets and… ratchet straps! I feel like you could essentially ratchet down your legs/hips/abdimen then get it around you in such a way that you could tighten and loosen around your shoulders by sticking out one hand.
A quick/dirty method you could try is by applying some glue in the gaps. Then wrap the whole dresser around with a couple of ratcheting tie down straps (example) to close the gaps. One somewhere in the middle, one near the top. Remove when the glue dried.
it's called a ratchet tie down, or ratchet strap.
I just linked to a set so you can see what they look like:
https://www.amazon.com/Ratchet-Tie-Down-Straps-Alternative/dp/B01F7KSAGI
You'll need a ramp and some ratchet straps. A set of four should do it - once he has the bike up in the bed, four points of contact should keep it pretty stable. Check these out from amazon and shop around:
Ratchet Tie Down Straps - 4 Pk - 15 Ft- 500 Lbs Load Cap- 1500 Lb Break Strength- Cambuckle Alternative- Cargo Straps for Moving Appliances, Lawn Equipment, Motorcycle - Includes 2 Bungee Cord https://www.amazon.com/dp/B01F7KSAGI/ref=cm_sw_r_em_apa_i_sopjEb9SHCKED
F2C 7.5 Feet Aluminum Foldable Loading Ramp/Truck Ramp/ATV UTV Ramp/Motorcycle Ramp/Trailer Ramp with Strap for Pickup Truck, Snow Blower, Lawn Mover, 750 Lbs Capacity(Single) https://www.amazon.com/dp/B07VMF7T5S/ref=cm_sw_r_em_apa_i_EqpjEbW97Q8YA