I am reseating a greenhouse on a concrete base - about 8ft x 6ft.

I will seat it on tanilized timber lats of say half inch x one and a
half inches - with rawl-bolts in the base - through the lats - and
then through the green-house base.

The base is not perfectly level - once side appears to be about half
an inch on the low side wrt the other three sides

I am minded to lay the wooden base lats on a mortar mix - just a skim
on three sides and then half-inch on the fourth.

Any points? - use a mortar mix or some other pre-prepared mastic or
similar - or even make as level as possible with mortar - let it go
off - and then lay all timber on mastic?

I intend to buy the tanilized timber lats - would you treat them any
more before use?