electric baseboard heater location

[MarkJKubicki]

I am in the process of winterizing a difficult to access beach-side summer home and have run into a quandary on where to place electric baseboard in the main living space (which will be the only area to have anything more than a space heater...)  Currently, the only insulation is in the roof (consequent of a recent replacement); otherwise, the sliding doors, walls, and floor are not insulated. 
None of the location options for baseboard heating are good; and I am looking for some insight on what would make the most sense (or no sense at all.)  (This is a VERY budget project, which dismisses some of the more creative possibilities.)

The total area to be heated is 650SF, and the units will be 240V

1) a temporary install utilizing removable curbs across 1 full (8ft) sliding door and 2 halves (2x 4ft) doors.  The units- would be plug-in to 240V outlets, and they and their curbs would be removed in the summer.

2) a temporary install  utilizing a removable curb across 1 full (8ft) sliding door, and across the front of a peninsula kitchen counter (6ft), (which would be under the counter's overhang.)  The units- would be plug-in to 240V outlets, and would be removed in the summer.

3) a permanent install across the only two clear walls; however, they are both fronted by couches (which could move in the winter -although not desirable.) This would be a permanent install.

4) a permanent install across 2 full (2x8ft) sliding doors (possibly ever 3), but under the floor between the floor joists, which would be closed in on the bottom, and have continuous linear grill (6" w x 96" long) across the floor opening of each.  (the floor joists are 10" deep at 16" O.C.) This would be a permanent install and the cleanest of the options; however, I'm concerned that the narrow floor opening will so restrict convection currents that they will be largely ineffective

ANY thoughts WHAT-SO-EVER will be greatly appreciated in advance
m.