I've got modular wheels on my 90 and the tyres are forever going flat? Can I run inner tubes to stop this? I've been advised not to and to put them in?? What's everybody's opinions on this? Cheers

If it says tubed or tubeless on the rims then do as is,

But first I'd advise you to get them tyres checked for slow punctures

Can cause problems with the tubes rubbing if rims not designed for them

That said if only used off road rather than at speed you'd probably be ok

Most tyres have cooling ribs on their internal surface... these tend to rub on the tube and cause further punctures... I found this out the hard way, and ended up sourcing tubeless rims.
Sounds like your tyres need the once over at the local tyre fitters...

Will be used mainly for off road use it's not my daily. There's not any punctures. When inflating the tyre I went round with soapy water and it was leaking all around the rim. Need to have a look at the tyres tbf see if they can have inner tubes.

Sounds like tubed wheels you've got. Though saying that I've put tubeless tyres on tubed wheels with no problems

Or get your tyre fitter to wire brush the seating area of the rim and used bead sealer, a thick black glue which fills the gaps and sticks the tyre to the rim.
If you are going to use tubes get Michelin or other good quality tubes or you may find the tyre will chaff the tube with a resulting rapid deflation.

as jacksta says if your soapy water has shown bubbles round the edge of the rim then it'll need the tyre taking off and the mating face of the wheel to the tyre cleaning up with a wire brush to remove the flaky paint and corrosion then for good measure they should use a tyre sealer instead of soap so that it'll help the tyre seal against the wheel. if they are too badly corroded you may be better off getting the wheels refurbed then fitting the tyre. my truck seems to have slow leaks and I have already cleaned and sealed one but it seems that I either haven't done a good enough job or I have further corrosion to deal with. as for tubes for road use as stated above for road use I wouldn't suggest it with wheels and or tyres that state they are tubeless as they do rub and they do deflate rapidly as the local enviro agency found on their defenders so they finally took our advise and fitted tubeless tyres to their tubeless wheels and we have only seen them once for a puncture since instead of their weekly visits with chaffed tubes failing on them usually from 30mph and above speeds according to the driver. for offroad use I can't see a problem with tubes for any tube/tubeless mix due to the low speeds and so lower tyre temperatures and the reduced risk of a sudden flat pulling you into a ditch or oncoming traffic