Permanently seal up - or not?

When we built my new greenhouse last year, the ground that we were building on was on a bit of a slope, so we built a base from treated timber which was chocked up at one end, with the other end (door end) being completely level - picture below shows it better than I can explain:



Now, as its been winter, my greenhouse is yet to get used in full anger - but, its not far off being pressed into service.

I was going to block up the gaps under the framework with ply or similar wood screwed onto the inside of the base - - however, I got to thinking that leaving them open would allow for easy cleaning (water run off) and could potentially help ventilation as I don't have any low down louvres (only four roof vents).

So, do I block them up permanently, or with something removable (not sure what), or just leave them as is?

 

Its managed to get through the winter without exploding, thankfully - must admit that is a point I never even considered.

I did wonder about mice etc getting in, so between that and slugs, it looks like I will have to do something permanent.

Hex - going by the heat that built up in there on the few warmish days that were left at the back end of the year, would the rigid insulation not make it too hot? Not sure about fixing it in place either really?
I do have some bubble wrap type insulation in the shed that has a foil backing that I could use, but again would it be too much heat wise?

I'll need to get some ply or something and get the saw out....

pete - its a 10ft x 8ft, so hopefully it will give me plenty of space to bring on my seedlings, and then later on will be a good space for my cucumbers, tomatoes and peppers. Not intending on using it for winter growing as yet, but in a couple of years once my outgoings settle a bit, I might just start heating it with an electric heater and get a real head start each year.

 

One side is bounded by the shed (until I move the shed) and the rear is bounded by the fence - maybe a 6-8 inch gap between the greenhouse and them. The doors are roughly north-west facing, so the main 'sunny side' is mostly west facing

 

I'll have a look at them and see if I can figure out how best they would fit etc before I go using the greenhouse in winter. Thanks

 

This might make it easier - this is an overhead view of my wee plot, with the location of the greenhouse drawn on, courtesy of Google, with the top of the pic being north.



Its in the shade in the morning (which is when this overhead must have been taken judging by the shadows being cast), and gets the sun in the afternoon onto one of the longest sides (slightly dappled with shade by the tree, which has now been trimmed quite a bit)