setting a new bath tub

[soloncamper]

I am installing a new whirlpool bath tub in a second story bathroom. There is no access to the bath from the first floor (at least not without tearing out the ceiling in the dining room.) The tub sits on a piece of OSB that restricts access to the tub drain from the side of the tub.

Question is: How do I get the drain assembly set into the trap without access? Do I set the trap and drain assemply and then place the tub onto the assembly and secure it? I don't see how I can get the drain assembly attached to the tub and then place it into the trap without access.
Might be a dumb question and I am not smart enough to realize the easiest way to do this, but I have onle installed one other tub and there was access from the side of the tub.

Thanks,

John

[pushkins]

Normally at the drain end of the tub you cut an access hole into the wall from the other side of the wall and install an access plate (sold at Lowe's/Home Depot etc...) this gives you access to the drain to make sure all fittings are tight and glued correctly.