It sounds as though the problem could be too much water and too little light. Seedlings that remain wet in a warm, humid environment will fall prey to diseases such as damping-off fungus. If your seedlings are collapsing at the base, that could be what’s happening to them. Excess moisture also can cause mold on the soil’s surface. Water from the bottom by adding water to the trays, and only add water when the soil surface feels dry to the touch. Your spindly seedlings may need more consistent light. Fluorescent shop lights provide an inexpensive source of steady light. Place one an inch above the plants as they first emerge. Keep the light turned on for 16 hours each day. Gradually raise the light source as the seedlings grow taller, keeping the bulb an inch or two above the uppermost leaves.