I don't have any reference with me, but I believe this is discussed in the book written by Kevin Starrett. I'll see if I can't check this evening (or maybe someone will beat me to it).
1). Laying on the passenger seat should be considered visible and not concealed. You might be able to get away with a holster between the passenger seat and the console so it doesn't slide around like it might on a seat. Having it on your person (open carry) is usually considered visible and not concealed, but this may cause alarm to the officer stopping you. Either way, I would be sure to disclose the information immediately. It is not required in Oregon, but it surely wouldn't hurt - especially as an out of stater.
2). If you look at the various cities of Oregon that have Open Carry (non-licensed) laws, empty would be considered: Nothing in the chamber (or cylinder), magazine removed and no rounds in any magazine. For example, if you were walking around downtown Portland... pistol on hip, empty magazine in left pocket, loose rounds in right pocket. No confusion and no ability to argue that you just emptied it.
If you get a change to pick up a copy of Kevin's book I would recommend it. Here's the info: http://oregonfirearms.org/store/uorlbk.html
A little more detail from the ORS:
166.250 Unlawful possession of firearms.
(1) Except as otherwise provided in this section or ORS 166.260, 166.270, 166.274, 166.291, 166.292 or 166.410 to 166.470, a person commits the crime of unlawful possession of a firearm if the person knowingly:
(a) Carries any firearm concealed upon the person;
(b) Possesses a handgun that is concealed and readily accessible to the person within any vehicle; or
(c) Possesses a firearm and:
(A) Is under 18 years of age;
(B)(i) While a minor, was found to be within the jurisdiction of the juvenile court for having committed an act which, if committed by an adult, would constitute a felony or a misdemeanor involving violence, as defined in ORS 166.470; and
(ii) Was discharged from the jurisdiction of the juvenile court within four years prior to being charged under this section;
(C) Has been convicted of a felony or found guilty, except for insanity under ORS 161.295, of a felony;
(D) Was committed to the Department of Human Services under ORS 426.130; or
(E) Was found to be mentally ill and subject to an order under ORS 426.130 that the person be prohibited from purchasing or possessing a firearm as a result of that mental illness.
(2) This section does not prohibit:
(a) A minor, who is not otherwise prohibited under subsection (1)(c) of this section, from possessing a firearm:
(A) Other than a handgun, if the firearm was transferred to the minor by the minor’s parent or guardian or by another person with the consent of the minor’s parent or guardian; or
(B) Temporarily for hunting, target practice or any other lawful purpose; or
(b) Any citizen of the United States over the age of 18 years who resides in or is temporarily sojourning within this state, and who is not within the excepted classes prescribed by ORS 166.270 and subsection (1) of this section, from owning, possessing or keeping within the person’s place of residence or place of business any handgun, and no permit or license to purchase, own, possess or keep any such firearm at the person’s place of residence or place of business is required of any such citizen. As used in this subsection, “residence” includes a recreational vessel or recreational vehicle while used, for whatever period of time, as residential quarters.
(3) Firearms carried openly in belt holsters are not concealed within the meaning of this section.
(4) Unlawful possession of a firearm is a Class A misdemeanor. [Amended by 1979 c.779 §4; 1985 c.543 §3; 1989 c.839 §13; 1993 c.732 §1; 1993 c.735 §12; 1999 c.1040 §1; 2001 c.666 §§33,45; 2003 c.614 §8]