Xbee serial link near ground level

[Cognito]

Hello!
This will be one of my first posts on this forum, which is almost a shame considered the length of time I has been registered on this forum. I have a lot to do, but anyway; I have (surely a ridiculous) problem with the communication between two Xbees.
This is my setup:
- xbee nr 1. Xbee Series 2 with 2mW wire antenna. Placed 150 mm above ground(178 mm with antenna) and 17 mm above a circuit board (35 mm with antenna). This radio is placed on a rover, whose intention is to drive semi-autonomously in occupied terrain.
- xbee nr 2. Xbee Pro Series 2B with 63 mW RPSMA connection. Placed inside a suitcase together with control unit, and attached with an antenna (here is where the troubles begin).

I have a few questions/problems, but I start with the most important ones:
 1: The Rover, ground station and firmware is still put-together prototypes, but is in the final stages before constructing a much better prototype. One of the tests I ran was aimed at increasing the range of the serial communication. I used the same setup as described, with a 2.4 GHz directional antenna (https://dx.com/p/2-4ghz-16dbi-directional-high-gain-16-unit-antenna-for-wifi-wireless-network-rp-sma-33016) thinking it would work... nope.

The two Xbees wouldn't establish a link whatever I tried. The antenna + coax works fine when used with other 2.4GHz applications. I'm obviously not seeing something, but I'm not and EE either. Hopefully someone of you are and/or are clever enough to think of something

2: When I started developing  this rover, I thought it would be nice to have the capability of more than point to point network. I have now however changed my mind and are wondering about converting to the 433 MHz 3DR radios. Is this a good choice?

3: The final Rover is supposed to be made from sheet metal, which is not the best material to transmit through. My first thought is that it can't have a long antenna sticking out of it, because it is supposed to work upside-down as well as upright (<-- correct terms ?). Do you have any thoughts around that and any methods to increase range, based on the fact that this is supposed to work in woods, flat areas and hilly terrain?

I can post some drawings or other material if this is helpful.
Any help and feedback will be graciously appreciated