How to Unlock 2nd Gateway Tunnel Snowrunner Season 9 Renew & Rebuild

I am on Xbox One, might you know why I can't load anything onto the truck bed? Have a 6 slot trailer but it won't led me use the 3 spots on the Twinsteer (after using 1 for the low saddle) maybe I need to be using the exact same trailer you are using?

UKGAMER808 after being annoyed at the crashes and losing my saves on this map I've started to play it again still getting crashes but the in game saves are working so not losing to much just put out the fires on Albney river the ware houses then I will try the railway station fires out iam on the ps4 version by the way only because of my game saves

Mate, what actual truck Mod are you using??