ERF MAN:
tachograph:
ROG:
I think I am correct in saying that a privately taxed LGV of any size only needs the tacho seal to be ok and does not need the regular inspections BUT I open to be told otherwise …I don’t know much about the tax but as the OP wants to use the vehicle to carry goods I doubt he can tax it private for private use.
Either way carrying goods will be in-scope of EU regulations so the tachograph will need to be used, and as far as I can see it will need to be inspected every 2 years.
That is unless he can find a way to carry his military vehicles on a 7.5t vehicle
If the vehicle is being used in connection with a business and the truck or van is over 3.5t gross combination weight you will need to use a tacho, if over 7.5t GCW you need an O license as well. It’s only private if your not earning any money such as attending a military show but not if your paid to be there. I know I send like I know what I am talking about but please don’t ask me to represent you in court. Dougie
For the EU regulations whether or not you’re being paid makes no difference to whether or not the tachograph needs to be used, if you’re carrying goods and the vehicle is over 7.5t it’s in-scope of EU regulations, even if they’re your own goods and you’re not being paid to transport them.
The point here is that the OP doesn’t just want to enter the vehicle in shows he wants to use it to transport his military vehicles, even if he uses the vehicle to transport his own military vehicle to and from shows it will be in-scope of EU regulations.
Having said that there may be one exemption from the EU regulations that the OP may wish to consider, I believe a vehicle over 25 years of age would be exempt from EU regulations and all tachograph rules 
Commercial vehicles that have a historic status according to the legislation
of the Member State in which they are driven and that are used for the
non-commercial carriage of goods.In the GB, a vehicle is a historic vehicle if it was manufactured more than 25
years before the occasion on which it is being driven.