Anne Welsh Jackson wrote:

We didn't hang about when we were erecting either of them.
Got 'em up, and masticked to the slab base. No probs! The mastic prevented the slugs accessing the 'house from
under the base as well...


We didn't hang about either we[1] built it twice, in the one day, once
as per instructions but 'too' well, parts that were supposed to slot
together didn't have spaces as we had constructed parts with no gaps.
Then we rebuilt it on the ground, we made little plates to screw the
bottom cill to the base. The gaps between this bottom cill and the slab
base was filled with a sand/cement (mortar) mix to keep out
'creepy-crawlies'.

[1] Myself and my youngest son (15)(who requires lots of support special
school all that)it is his greenhouse (his as he saved up for it he was
too old for toys so at birthdays and Christmases he got money for
presents until he had saved enough to get a greenhouse) really he is the
gardener I just fumble about and do what he tells me.
He started of with a ½m x 2m patch in the garden, next year I
extended it a bit for him, we sent photos. of this patch and what he
grew in it to Blue Peter, he got a BP badge. This patch has grown (no
pun intended) again plus he has the hanging baskets, the greenhouse and
he looks after the tubs out the front.

ASIDE :- Just had a thought one of these days I will have to put
together a web page of what was done.