I've mine insured with autoline. E46 M3 is insured as classic and E30s added on them too.
Going to look into adding the X5 to it soon too while might pick up a Golf GTi or something for my fiancée and insure that as my main car if the commercial insurance on my Defender doesn't work as the main policy for classic insurance.
Only limitation is the mileage limit obviously which could be an issue.
Looked into trade policies but with a farm and stuff, it gets very awkward for me with dual usage and stuff like that and you can have issues if anything ever happens outside of business hours or on a trip away etc