Hey Mike - have you tried the woodland scenic's water? The liquid type? I've used it before and it's fairly transparent - the only downside as I recall is that it shrinks a little - so you might get some separation around the edges. I don't know if I'd try something really deep, but you might try(?) something deep enough for your truck - maybe the roof can stick out above the waterline?
Have you checked model railroad forums for ideas? Folks often have pretty vast expanses of water on the big layouts. I remember reading of various methods for achieving very good "fake" water...you might just need to experiment until you get the look you're after.
In thinking about this, if you are representing a fairly big frozen lake, and snowy conditions, maybe only the area immediately enclosing the truck needs to look like "water" per se - so, you might consider, building a canal/wall around the area with the truck in it, and fill only that area with your fake water - the rest of the lake or pond surface could then be made of any other material - essentially like a deck around a swimming pool - which you will cover with "snow", so you won't be able to see what it's actually made of once you're done (and, you can paint it white before adding your snow - it will likely look a lot like a snow covered frozen surface)
...remember tho, in any event, make sure your "water" area is completely water tight!!! The "fake" water, like real water will escape when you pour it in if you don't have it all sealed! Yes, it will! I've, uh seen it!!!! For a while I had a beautiful "stream" crossing my shop floor!!!
One more thing - you might consider a fairly light color for the stones, sand, mud etc on the bottom of your lake - if you choose a dark color for the base, it might be difficult to see your truck, there might not be much contrast and it might just look like a dark shadow from above - unless of course you decide to leave the roof or some portion of the bed above the pour/level line of the water. I have been surprised by how transparent the fake water is - but, I haven't tried it much more than an inch or so deep - in that case, you can easily see through the water material to your base material - like in a stream, you can easily see rocks and sand.
Or, do something else!
Keep at it!! This sounds like a cool dio! Sorry about the chilly pun!
Take it easy and keep us up on your results!
Nick