Have you contacted M&H to ask if they can supply the tubes?
The tubes actually add an extra bit of support to the sidewall and tire as a whole, in my opinion. Without them, street-driving is interesting, especially around corners. But, they LOOK cool.
Slicks for regular use can pose problems. I kept mine off the car for the track only.
As you mentioned, the air pressure loss is a problem. Obviously, you'll need to keep the rear of the car on jack stands, or dedicate yourself to filling the religiously. You might consider checking them for leaks in a tub of water. I had a pair mounted tubeless once ... they wouldn't seat on the rim so I used silicone as a 'lubricant' ... may have helped the seal as they almost never needed refilling when stored/garaged.
If you do get tubes, you'll have to drill out the valve stem hole to fit the stem. Now they're dedicated slick rims ... or at least, potentially tube dependent or PTD.