Dan
   I also used plexiglas for my lehman. I have it situated on a concrete slab
so I was collecting moisture thru the slab. I eliminated this by placing some
visqueen under the sensor and cover. I don't have a problem with temperature
and the lehman.  For creatures my thought was to put soft 1/2" wide foam
stripping under the perimeter edge of the cover (sticky on one side) . The
weight of the cover seems to seal the minor surface irregularities of the slab
and hopefully preventing the entry of insects. I do have a big problem  with
the horizontal force balance and the vertical smt-8 style sensors wrt
temperature and air currents. I think this is because the lower frequencies of
the signal are amplified to correct for the drop off of the sensor. I have the
best luck with air gradients by keeping the temperature as constant as possible
with heavy insulation.This is also needed for the temperature affects on the
leaf spring. I have the smt8 in a tightly fitting home-made aluminum box.
Outside this box is ~3" of air then 1" thick foam followed by 3-4" of batt
insulation and another 1" of foam. Makes the needed sensor space a little large
though. One of  these days I'll  have an underground vault where I can keep the
sensors and plenty of wine :)
Regards
Barry

dan stevens wrote:

> When building a cover for my Lehman what considerations should I take into
> account? Obviously air currents are the main thing I'm trying to cut out,
> but what about temperature and critters? The seismo is located inside a
> windowless room that is kept at a constant temperature year-round. I'm also
> hoping to use plexiglass, glass, or anything that I can see through. Is the
> thickness of the material used very crucial? Does anyone have any
> pre-construction tips or pointers that would be helpful?
> -dan

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