It will normally take a well charged battery to run the landing gear or slides. For these large draw items, the power through the converter is not enough on it's own. Plugging into truck can help, but again, not a strong power source, with the small wires connecting. You can use heavy jumper cables from truck to camper battery to operate landing gear.
Also, there should be a square type circuit breaker, very near the battery (follow wire coming from battery) that may have tripped. It should reset, but may need replacing. It may be located on the basement inside wall near battery.
Jerry