Hiscocks do professional indemnity insurance about £150 a year for TMs. Professional indemnity insurance
Most important things in your contract are: fees, contract duration and termination clauses. Your strongest bargaining is at the start of your contract not when you are appointed as TM. An operator can drop their TM with no negative impact, quite the reverse. If you quit because they don’t pay you they can apply to the TC to have a 6 month period of grace to replace you, during this time they don’t have to pay anybody anything. You must have a contract that you can use to sue for your fees after the event. If you don’t feel you can write your own contract maybe you are not ready.
If you want to be TM to ODs who have lots of experience as drivers themselves, then you may be okay. But I think you should work as a TM first before offering your services to others, the CPC exam doesn’t cover much.
Just my thoughts