Stakin' in the rain, what a glorious feeling!
If you think a lath bag is going to keep you wood dry then it really is not raining. After a couple of hours of good old Pacific NothWet sunshine nothing is dry. Wet wood and notes are the least of the problem. Everything is usually covered in a thin film of mud.
If it's any consolation, down this way we use an umbrella, over the total station, as a sun shade.
On a side note, Kiel does not melt easily. I got one stuck in the defroster, and despite running the thing all shift to dry gloves while I worked in the "wintery mix" it's still stuck!
Good looking out not putting a sail next to your total station. I mentioned to my boss that I used the popup tailgate on our yukon to protect the instrument and man from hard rain, when she purchased a transit connect. Her response was to purchase a 6' square popup pavilion to protect the instrument.
Need less to say in a beach community... it was never used for that purpose.