Go for a "plated" trailer, not some "welded by a mate who knows his stuff" abortion. I think French Police are keen on seeing plated trailers.
Bikelug and similar are attractive, but if you look to transport 2 bikes - no.
Even if you have a fixed light board - if you are leaving the trailer outside, get a removable light board and fit it only when you are going to use the trailer. Easier for testing too.
Try and avoid those bar-end strops - there are a lot of expensive controls on the bars these days, that could get damaged.
Use cargo straps on the forks/clamp, ensuring that they are protected from chafing.
Use a cloth on the front rim and tighten a small ratchet-strap to pull the front wheel into the wheel socket.
Don't use those open-hooks on ratchet-straps. Use decent carabiners which can't unhook if the bike bounces about on potholes etc.
Don't cover the bike on the trailer - the covers at best will flap around, rip and mark paintwork edges. At worst - they can wear away the bike paint on panel edges!
Consider one of those rear wheel clamps (bearing in mind you will have to remove the hugger and exhaust can to do so) - as that secures the unsprung bike. It takes only 5mins to remove my XR can and hugger. (don't forget to bung
them, and the tools into the car)
Pack extra ratchet straps and grip straps in the car, in case you require additional.
Use re-usable cable ties for:
1. Securing the ratchet handles to the bodies.
2. securing folded-up strap tails to the cargo straps.
3. making sure that the trailer safety chain/wire - is secured in place so that in event of a ball detachment, the chain/wire doesn't jump off.
With bike trailers being very rudimentary in the suspension area- when the trailer is 'jiggling' about - the bike will also. If the bike doesn't appear to be doing that - it might be starting to loosen.
Some people even use a reversing camera (aftermarket) and instead of powering from the reversing lamps - mount a switched supply and they can keep an eye on the trailer/bike low-down any time they want during the journey.
When you set off on a long journey - stop after 20 miles and check over the securing arrangement.
Take photos of the arrangement. Then, if it proved to be satisfactory - you can refer to that next time.
Last but not least: When you have finished securing the bike to the trailer - push it to and fro and declare:
"That's not going anywhere" 